Method for removing corrosive substances from hydrocarbons



W. MILLER May 19, 1936.

METHOD FOR REMOVING CORROSlVE SUBSTANCES FROM HYDROCARBONS Filed May 7, 1934 NUHA Patented May 19, 1936A i 2,041,364

UNITED STATI-:s PATENT oFFlc METHOD FOR REMOVING CORROSIVE SUBSTANCES FROM HYDROCARBON S Walter Miller, Ponca City, Okla., assigner to Continental Oil Company, Ponca City, Okla., a corporation of Delaware I Application May 7, 1934, Serial No. 724,331 3 Claims. (Cl. 15M-24) My invention relates to a method and appara- Company the price reduction for hydrogn sulphide tus for removing corrosive substances from hy- Content is not as great as that for the presence drocarbons and more particularly to a method of corrosive mercaptans. The mercaptans in the and apparatus for removing corrosive mercapgas are not removed by ordinary bog ore treat- 5 tans from gases and liquids resulting in the rement, which is one of the cheapest and most com.4 5 lining of petroleum, I monly employed methods used for removing hy- Many crude oils occurring in the United States drogen SUllJhide- If COIIOSV@ mercaptans are a1- may run as high as four percent by weight or gas, and particularly on copper and brass housel0 ring type sulphur compounds, and free sulphur, One object of my invention is to provide a The hydrogen sulphide and 10W molecular Weight method and apparatus for the removal of corle mercaptans in crude oil or in products resulting IOSlve mercaptans from hydrocarbon gases prior and mercaptans formed by the conversion of other hydrocarbon liquids which at times are used for Sulphur compounds which may be present in the generating gas or enriching other low thermal heavy topped products. value gases.

Hydrocarbon gases resulting from petroleum ell Still another object of my invention is to prorefining are suitable fuel for elly gas mal-ns and vide a method of removing corrosive mercaptans 25 generally desirable for fuel consumption A gas Without the additional expense of removing hycompany selling gas Obtained from oil renen-es drogenssulphide which may be removed by cheaper will usually process it to remove hydrogen sulphide methodsif the gas contains an excessive amount, before Another object of my invention is to provide a 3e it is delivered to the consumer. There are a nummethod of removing mercaptans in Which hydro- 30 her of methods known for removing hydrogen een sulphide may be removed or partially removed sulphide from gas. Among these are the bog ore Without the aid of Chemical treatmenttreatment and alkali Washing. The methods used other and fiiithei objects of my invention Wiii for removing hydrogen sulphide do not, as a rule,7 appear from the following description.

T35 remove corrosive mercaptans. Those methods The accompanying iigiiie is a' diagrammatic 35 which do remove corrosive mercaptans are costly yieW of one form of apparatus' eapohie of carry in their operation. Gas distributing companies ing out the method of my iiiyehiiehwhich produce gas from oil reneries often base in general' my invention contemplates comen' the purchase price on the hydrogen sulphide @en trating corrosive mercaptans from a large voltent and/or the corrosive mercaptan content. iiine'of gases into a iiqiiid produce substantiel' There may be a very definite prescribed maximum iy iiee of hydrogen siiiphide- The concentratallowable percentage of either the hydrogen suling Steps 0i my hi'eeess maybe carried out by phide or mercaptan` content in gases which are absorption and fractionation. The concentrated received by gas com a'nies. The purchase price liquid containing the corrosive mercaptans is per unit of volume or" gas may decrease rapidly then treated with an alkaline or other mercaptan as the hydrogen sulphide and/or corrosive sul- 'emOVins agenl- The mercaptan free liquids are phur content increases. It is, therefore, desirable then used as enriching oils or converted into for oil refining companies to be able to supply gases and used for enriching purposes.

a gas to gas distributing companies having a low More particularly referring now to the draw- 50 content of corrosive mercaptans and/or hydrogen ing, a pressure distillate Obtained from Cracking sulphide. Small percentages or traces of mercapunits is charged through line l by pump 2 to a Since hydrogen sulphide may be removed comtillate is withdrawn from the tower through line g5 parativelyyeasily with little expense by the gas il. Ihegas withdrawn from thestabilizer thro e5 line 5 may consist, for example, of methane, ethane, propane, smaller pentane and heavier hydrocarbons, hydrogen sulphide, and low, boiling mercaptans. It is understood that isomers of these hydrocarbon compounds and other unsaturated derivatives of each, boiling at sim'lar temperatures, will be found. The gas and/or vapors are cooled in cooler B and passed into accumulator 1 from which reflux is taken and pumped by pump 8 through line 9. Gas from separator I0 passes through line II and joins gas from accumulator 1 coming through line I2 and the combined gases pass through line I4 to the absorber tower I5. Other gaseous hydrocarbons containing hydrogen sulphide and/or mercaptans may be charged into the line I4 going to the absorber I5 through line I6. Lean absorber oil enters the absorber I5 through line I1. The enriched absorber oil is pumped by pump I8 through line I9 to a steam still 20 which is provided with a heating co'l 2I supplied by steam through line 22. This absorption step is operated to remove substantially all gaseous mercaptans and give a lean mercaptan free gas through line 23. The gas being removed from line 23 will consist of methane, ethane, small amounts of propane and butane, and hydrogen sulphide. The absorber I5 is controlled to obtain substantially all of the corrosive mercaptans in the rich oil. The enriched oil is stripped of all the absorbed materials in still 20, the lean oil being pumped from the still by pump 24 through line I1 to the absorber. The vapors and gases stripped from the rich oil in still 20 are withdrawn from the still through line 25 and passed through condenser 26 which is supplied with cooling water through line 21. The volatile gases and lighter ends which are not condensed in condenser 26 are withdrawn from separator I0 into which the liquid products of the cooling step are discharged, through line I I. The less volatile liquefied fractions of the gaseous hydrocarbons and all of the mercaptans are removed from the separator III through line 29 andpumpedby pump 30 to a primary stabilizer 3I in which reboiling and fractionation takes place, heat being supplied through any suitable means such as a steam coil. Due to the differences in boiling points between hydrogen sulphide and corrosive mercaptans, it is a simple matter to obtain by fractionation in primary stabilizer 3| a liquid containing the mercaptans and free of hydrogen sulphide. This liquid is Withdrawn from the primary stabilizer through line 32 in the form of a light gasolinelike material. The gas withdrawn from the primary stabilizer through line 33 will contain -methane, ethane, small amounts of propane and the like, and su'ch hydrogen sulphide as was not removed in separator IB. It will be practically mercaptan-free, the mercaptans having been separated by fractionation and being contained in the light, low boiling gasoline withdrawn from the stabilizer through line 32. This light gasoline is then treated by a treatment designed to remove mercaptans. It may be passed through a body of caustic contained in caustic wash tank 34 in which the mercaptans would be removed without spending caustic for the removal of hydrogen sulphide. It will be obvious that, if hydrogen sulphide were present in the liquid being treated, caustic would be spent in removing hydrogen sulphide which can be more economically removed by other methods.

As pointed out above, I desire to selectively remove the mercaptans in an economical manamounts of butane,l

My invention is not limited to ner. The light gasoline, free of mercaptans, is then pumped by pump 35 through line 36 to the final stabilizer 31 in which fractionation takes place, heat for reboiling being provided by coil 31'. The gas and vapors removed from the final stabilizer through line 38 are condensed in condenser 39 which is supplied with cooling water through line 40 and passed through line 4I to a separator 42. The more volatile hydrocarbons are removed from the separator through line 43. This gas contains the balance of the methane, ethane, propane, and like boiling hydrocarbons and iso-butanes. This gas will be hydrogen sulphideand mercaptan free. Corrosive mercaptan-free liquid may be withdrawn through line 5U without going to stabilizer 31, if final stabilization of liquid is not required.

The stabilizing tower 31 is so controlled as to give a light gasoline of predetermined vapor pressure. This is withdrawn from the tower 31 through line 44 and may be used as an enriching oil or as casinghead gasoline for gasoline blending. The less volatile hydrocarbons condensing in condenser 39 accumulate in separator 42 and the liquid is used as reflux being pumped from separator 42 through line 45 by pump 45 and line 41 by pump 48 as reflux for stabilizers 3l and 31 respectively. This can be readily seen by reference to the drawing. The total liquid in 42 may be vaporized and mixed with other mercaptan-free gas.

If desired, the gases from lines 23, 33, and 43, and/or liquid from line 50, may be combined as a salable gas, substantially free of mercaptans,

hydrogen sulphide. If a hyfree gas be deliquid from line drogen sulphide sired, the gas from line 43, or

50, may be held separate from the gases from' Due to pressure of the the Very high vapor product being treated in my invention, I prefer to throughout the entire operation.

any degree of pressure in any of the particular steps, since variations in the types of materials being handled will determine the pressures and temperatures to be carried at the various steps of my process. For example, absorption tower I5 may be operated at pressures as low as 25 pounds per square inch. Higher pressures as a rule are employed and may be as high as 500 pounds per square inch or more. Similarly the stabilizers and stills may be operated at pressures as low as 25 pounds per square inch. As a rule, higher pressures are desirable and more economical. Pressures pounds per square inch or more may be employed in the stabilization steps as practiced in stabilizer stills 3I and 31.

As a particular example of the operation of my process, I have taken the gas from a renery processing West Texas crude and producing approximately 3.5 million cubic feet of gas per day. The gas was comprised by fresh gas from Dubbs and Cross cracking plant operations. Gas was also USE pressure as high as 1003 b taken from a debutanizer operation, from a steam 75 still recycling step, from crude oil distillation and storage tanks.

'I'he composite gas had the following average Corrosive (mercaptans), 10 mg./cu. ft.

The absorber was operated .at 53 pounds per square inch pressure, and employed 65 gallons per minute of 70 F., 35 A. P. I. gravity absorber oil. The residue gas from the absorber had the following composition:

Lean gas i Percent Methane 45.80 Ethane 24 15 Propane 21.65 Butane 1.65 Pentane and heavier Trace Hydrogen sulphide 4.90

Corrosives (mercaptans), 2.5 mg./cu.lft.

It is to be noted that a more efficient operation in the absorption step will reduce the mercaptan content of thelean gas.

The distillation of the rich oil in still 20, taken from the absorber l5, which distillation was carried on at 65 pounds per square inch pressure, yielded 600 barrels per day of a product having the following approximate composition by volume:

Liquid absorbed Percent Propane 15.60 Iso-butane 13.49 Normal butane 38.30 Pentane 20.36 Hexane and heavier. 12.25

This liquid contained all of the corrosive mercaptans absorbed in the rich oil and a small amount of hydrogen sulphide. 'I'his liquid which corresponds substantially to the liquid being withdrawn from separator I by pump 30 is stabilized in the primary stabilizer 3l to remove the hydrogen sulphide in the gas, the stabilizing step bein-g so carried on as to leave the organic corrosive mercaptans in the liquid. I accomplish this under 225 poun-ds pressure using a temperature of 220 F. as the bottom temperature in the stabilizer 3l and a final gasseparation temperature at the stabilizer top of 90 F. The average yield of liquid withdrawn from the stabilizer 3l was 450 barrels a day. The gas withabout 200,000 cubic feet per day and had the tributing company in a more 3 Liquid Percent Methane .00 Ethane .00 Propane 12 54 Iso-butano 7.61 Normal butane 41.15 Pentane 22.55 Hexane and heavier 16.10 This liquid also contained all of the corrosive mercaptans not escaping with the gas through `line 23. This liquid was then given a caustic wash in tank 34. The liquid was then given a final stabilization in still 31. The nal stabilization operation was 210-220" F. and a final gas separation temperature at top of still of 90 F. The quantity of gas removed from separator 43 `was about 100,000 cubic feet, having the following approximate analysis;

Percent Methane .00 Ethane .00 Hydrogen sulphide .00 Propane t 62.75 Iso-butano 13.80 Butane and heavier 23.45 Corrosives (mercaptans) Trace 'The liquid Withdrawn from the stabilizer still 31 through line 44 was substantially propane free and having suilcient iso-butane and normal butane removed to give the vdesired vapor pressure. The final liquid contained little or no corrosive mercaptans and is a desirable enriching oil capa# ble of being used to enrich low B. t. u. gas without. encountering objectionable mercaptan corrosion.

`It will be seen that I have accomplished the objects of my invention. I am enabled to remove a substantial amount of mercaptans from heavier gases by absorption and to concentrate the mercaptans in liquid which may be economically treated for mercaptan removal, which liquid may be subsequently used for generating or enrich' ing low B. t.-u. value gases. I am enabled to remove corrosive mercaptans without the necessity of using a large quantity of alkali for the removal of hydrogen sulphide which may be more economically removed by other methods. I am enabled to separate hydrogen sulphide from normally gaseous hydrocarbons without the aid of chemical treatment. I am enabled by my process to deliver refinery gases to a purchasing gas dissalable and less objectionable form.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the speciic details shown and described.

Having thus described my invention, what I claim is:

1. In a method of removing sulphur compounds irom cracked hydrocarbons, subjecting the hydrocarbons to an absorption step in which the hydrocarbons are contacted with an absorption medium, distilling the absorbed hydrocarbons and sulphur compounds from the absorption medium, subjecting the gases and vapors from the distillation step to fractionation, controlling the fractionation step so that hydrogen sulphide and lighter hydrocarbons are in a gascous state While-the heavier sulphur compounds and heavy hydrocarbons are in a liquid state, withdrawing the hydrogen sulphide and lighter hydrocarbons from the fractionatlng zone, separately withdrawing the heavier hydrocarbons containing heavier sulphur compounds from the iractionating zone, subjecting the heavier hydrocarbons to a sulphur removing treatment, stabilizing the thus treated heavier hydrocarbons and recovering a rich hydrocarbon gas and a lightihydrocarbon liquid from the stabilizing zone.

2. In a method of removing sulphur compoiuids from cracked hydrocarbons, subjecting the hydrocarbons to an absorption step in which the hydrocarbons are contacted with an absorption medium, controllingthe absorption step so that most of the hydrogen sulphide is not absorbed, distilling the absorbed hydrocarbons and sulphur compounds Ifrom the absorption medium, subjecting the gases and vapors from the dis tillation step to fractionation, controlling the fractionation step so that hydrogen sulphide and lighter hydrocarbons are in a gaseous state while the heavier sulphurcompounds and heavier hydrocarbons are in a liquid state, withdrawing the hydrogen sulphide and lighter hydrocarbons from the fractionating zone, separately withdrawing the heavier hydrocarbons containing the heavier sulphur compounds from the fractionatng zone, subjecting the heavier hydrocarbons to a sulphur ,removing treatment, stabilizing the thus treated heavier hydrocarbons and recovering a rich hydrocarbon gas and a light hydrocarbon liquid from the 'stabilizing zone.

3. in a method of removing sulphur coinpounds from hydrocarbons, drocarbons to an absorption step in which the hydrocarbons are contacted with an absorption medium, controlling the absorption step so that most of the hydrogen sulphide is not absorbed, distilling the absorbed hydrocarbons and sulphur compounds from the absorption medium, subjecting the gases and vapors from the distillation step to fractionation, controlling the fractionation step so that hydrogen sulphide and lighter hydrocarbons are in a gaseous state while the heavier sulphur compounds and heavier-hydrocarbons are in a liquid state, withdrawing the hydrogen sulphide and lighter hydrocarbons from the fractionating zone, separately withdrawing the heavier hydrocarbons containing the heavier sulphur compounds from the fractionating zone, subjecting the heavier hydrocarbons to a sweetening treatment, stabilizing the thus treated heavier hydrocarbons-and recovering a rich hydrocarbon gas and a light hydrocarbon liquid from the stabilizing zone.

WALTER MILLER.

subjecting the hy' 

